Light emitting diodes (LEDs) are useful in a wide variety of applications. An LED array is an array of LED die mounted on a common substrate. LED arrays are used as light sources in an increasing variety of applications including communications and instrumentation; commercial and household room lighting; and automotive and visual displays. LED Arrays are devices comprising a plurality of LEDs on the same substrate. LED arrays can be made by a variety of techniques.
One problem with LED arrays is the significant heat generated by dense concentrations of LEDs. Solutions to the thermal problems associated with LED arrays are the subject of a related application entitled “Light Emitting Diodes Packaged For High Temperature Operation”, U.S. patent application Ser. No. 10/638,579, filed Aug. 11, 2003. Another problem associated with LED array performance, illumination efficiency, is the subject of a related application entitled “Efficient LED Array”, U.S. patent application Ser. No. 10/822,191, filed Apr. 9, 2004. These two applications are both hereby incorporated herein by reference.
LED arrays have been successfully fabricated using low temperature co-fired ceramic on metal (LTCC-M) packaging technologies. The LTCC-M structure and materials are described in U.S. Pat. No. 6,455,930, “Integrated Heat Sinking Packages Using Low Temperature Co-fired Ceramic Metal Circuit Board Technology” (issued Sep. 24, 2002) LTCC-M construction is further described in U.S. Pat. No. 5,581,876 (issued Dec. 10, 1996), U.S. Pat. No. 5,725,808 (issued Mar. 30, 1998), U.S. Pat. No. 5,953,203 (issued Sep. 14, 1999) and U.S. Pat. No. 6,518,502 (issued Feb. 11, 2003). U.S. Pat. Nos. 6,455,930, 5,581,876, 5,725,808, 5,953,203, and 6,518,502, all of which are assigned to Lamina Ceramics Inc., are also hereby incorporated herein by reference.
In many applications it is advantageous to control LED arrays with an electronic driver circuit. The driver can either turn the LED on or off, or it can control the output luminosity. Active power semiconductors can be used to provide the driver function. The driver control signal can be simply an on-off command, typically in the form of a low level control or logic signal. Alternatively, the control signal can be an electrical signal that sets the current flow through the LED for the desired luminosity. Where LED current is controlled to set the luminosity of the LED array, it can be further advantageous to include feedback and control circuitry. A photodetector component can be located near the LED array to measure its light output and to provide the needed feedback signal. The problem is the cost and complexity of the additional detector and the mechanical construction required to mount it in or near the array.
It would be highly advantageous to provide LED arrays with an on-board electronic driver and control circuitry including sensors for feedback control. Such circuitry is needed but has been difficult to package on the same substrate as the LEDs. Typically, the LED driver and control circuitry for a particular application are built on a printed wiring board (PCB) external to the LED array. This is problematic for applications that must fit into small spaces. LED arrays using external PCB mounted electronics are also costly. Previous attempts to incorporate driver circuitry into LED array packages have largely been unsuccessful because of the mechanical stresses caused by differences in the thermal coefficients of expansion between semiconductor die and prior art LED packaging methods and materials.
Accordingly, there is a need for an improved LED array devices wherein a less expensive driver, control circuitry, and a photodector sensor can be co-packaged within the array.